Answer to Question #13641 Submitted to "Ask the Experts"
The following question was answered by an expert in the appropriate field:
I recently went to the dentist who said I needed an orthopantomogram (OPG) x ray. I have some questions regarding the procedure.
- Is it necessary to wear a thyroid shield and lead apron when a dental OPG is taken?
- Are eyes and brain affected by dental OPG x-ray?
- Is a dental OPG safe for a child?
While the "dental OPG" terminology is used frequently in several countries, it is not common in the United States so I will define it for others who may not know the term. "OPG" was the brand name of a specific dental panoramic x-ray machine, the OrthoPantomogram. That machine has not been made for many years and in the United States the term "panoramic radiograph," sometimes shortened to "pano" or "pan," is more typically used.
In order to answer your questions, I would like to explain briefly how the panoramic radiograph is made. A very narrow slit of x rays travels around the back of the patient's head, roughly from one ear to the other (it does not make a complete circle around the head) while the digital sensor or film cassette moves around the front of the patient. Even though it takes 12–20 seconds to expose the image, depending on the specific machine, only a tiny fraction of the head is being exposed at a time due to the narrow beam. The x-ray beam has a slight upward tilt in order to provide the best image. Of all the x-ray techniques available to image the teeth of both jaws and some surrounding tissue, like the jaw joints in front of the ear, panoramic radiography requires the lowest radiation dose.
Now to your specific questions:
- A leaded thyroid shield is NOT recommended for use during panoramic radiography. Because the x-ray beam goes around the back of the head with a slight upward angle, a shadow of the thyroid shield gets projected over the lower front teeth, essentially hiding them from view. The leaded apron, however, will not interfere with the image because it is not in the path of the x-ray beam. Because the radiation dose from panoramic radiography is so low and the beam is aiming upwards, it is not necessary to use the leaded apron. However, many dentists and patients feel more comfortable using it and for that reason it is typically offered.
- Regarding exposure of the eyes and brain, it is unlikely that the brain will be exposed due to the vertical size of the x-ray beam and its location focused on the jaws. The eyes may be in the path of the very top edge of the x-ray beam, depending on the size of the patient, but because the beam comes in from the back of the head, there is no direct exposure to the eyes.
- Regarding whether it is safe for a child to have a panoramic radiograph, the answer depends on why it is recommended. Radiographs of all types, whether they are dental or medical, should only be taken if there is a clinical need for the information they provide. If the child has dental problems detected clinically (for example, large cavities, swelling, pain, or abnormal tooth or jaw development), a panoramic radiograph may be a good imaging technique and could be considered safe. However, if the dentist does not detect any problems clinically and the patient has no symptoms of any kind, most dental authorities, including the American Dental Association, would recommend no radiographs for very young children. For that reason, if your child's dentist (or your own dentist) wants to take x rays, it's a good idea to ask why. If there is a reason other than "we just want to see what's there," it is safe to go ahead with the x rays. Note: there is a reason for taking bitewing radiographs (used to check for cavities between the teeth) periodically even if no cavities are seen because they frequently cannot be found with a clinical examination until they get very large and more difficult to deal with. The frequency of x rays depends on the patient's oral health and risk of developing cavities. For many adults once every two to three years is appropriate, while some patients with many cavities may need x rays every six months.
I hope that I have answered your questions satisfactorily (and provided a little extra information, too).
Sharon L. Brooks, DDS, MS
Professor Emerita, University of Michigan School of Dentistry
Dip., American Board of Oral and Maxillofacial Radiology